But in practice it's easy to run into roadblocks. Adopting healthy eating and exercise habits can be difficult. It takes time and effort to work physical activity into your daily routine. A good diet can be your road map to safe and effective weight management. Conversely, a poor diet can leave you spinning your wheels — or, even worse, pose serious health problems.

Components of an effective weight-loss program must include:

• A healthy diet that helps you select, prepare and eat healthy foods.
• An exercise plan that helps you increase your activity throughout the day as well as incorporate a more rigorous exercise period several times every week.

Weight-loss programs come in many forms today. Some prey on the desire for a quick fix, and some of these diets do help you lose weight quickly — at least for a while. But maintaining a healthy weight isn't something that most people can manage quickly and maintain over the long haul. It's a process, and it can be tough, but it's not impossible. If you're ready to commit to lifestyle changes — eating healthier and being more physically active — then you're well on your way to achieving a healthier weight.

The benefits of living at your healthy weight are numerous. You'll look better and feel better, and you'll probably live longer, too. But it's important to find a program that's safe and works effectively. Do some research before jumping into a new diet routine. If you have questions, talk to your doctor or nutritionist.

If you're considering a new weight-loss plan, evaluate it by the following statements to see how the program holds up. If one or more of these apply, raise a red flag.

• Promises of a quick fix
• Dire warnings from a single product or regimen
• Claims that sound too good to be true
• Simplistic conclusions drawn from a complex study
• Recommendations based on a single study
• Dramatic statements that are refuted by reputable scientific organizations
• Lists of "good" and "bad" foods
• Advice given to help sell a product
• Opinions based on studies published without peer review
• Recommendations from studies that ignore differences among individuals or groups

Here, in alphabetical order, is a bird's-eye view of some popular weight-loss plans — with a look at their premises, their founders or main backers, and what the scientific evidence shows. Take a look at each and use the list to figure out which are the healthiest programs to follow. Then talk with your doctor about a weight-loss program that's right for you.

The list is divided into two categories — weight management programs and diets, an important distinction to make. A diet helps you decide what and how much to eat, while weight management programs often include physical activity and behavior change in addition to your dietary plan.

• Body-for-Life (Bill Phillips)

  Premise: A 12-week fitness plan in which you eat a high-protein diet and exercise regularly. Phillips, a bodybuilder and entrepreneur, emphasizes portions, not calorie counts. You eat six meals a day — each meal consisting of one portion of protein and one portion of carbohydrates — and add a vegetable to two of the meals. Once a week, you’re allowed a "cheat" day to splurge on your favorite foods.

  Facts - This program's success is based on testimonials and anecdotal evidence. Although Body for Life emphasizes low-fat foods, the diet doesn't consist of enough variety for a truly healthy diet to meet all of your nutritional needs. (gee, where have I heard this??)

• Lifestyle Program (Dean Ornish, M.D.)

  Premise: Combines vegetarian and low-fat diets. Encourages high-fiber foods and limiting processed foods, such as cheese. Also recommends a daily exercise program. Dr. Ornish is the founder, president and director of the nonprofit Preventive Medicine Research Institute and has published numerous books about reversing heart disease through diet and exercise.

  Facts: There's moderate evidence that cholesterol levels may decrease and that this diet is effective for weight loss. It combines — as all effective weight-loss programs do — a healthy eating plan with regular physical activity. There's also good evidence that it can treat and possibly prevent heart disease, though some people have questioned its practicality. Many people can't follow a 10-percent fat diet long-term.

Facts: Limited-choice diets — diets that require you to eat a certain food repeatedly — are historically difficult to maintain. It can be challenging to drink and eat the same food over and over again. However, research shows that the continued use of Slim-Fast products can sustain long-term weight loss in overweight and obese men and women. Participants in a university-based study improved several risk factors for diseases that are strongly associated with excess body weight — risk factors such as high systolic blood pressure and excess lipids, lipoproteins and blood sugar (blood glucose).

• Carbohydrate Addict's LifeSpan Program (Drs. Richard and Rachael Heller)

  Premise: Richard and Rachael Heller claim that an excess of insulin, the "hunger hormone," causes the carbohydrate addict to experience intense and recurring cravings, as well as the heightened ability to store fat. The affected person has a biological condition caused by a hormonal imbalance, which can be corrected by following their program. They advocate a very low carbohydrate diet throughout the daytime, and a single "reward meal" consisting of carbohydrate counterbalanced by vegetable and protein.

  Facts: The effects of a low-carbohydrate diet may result in eating high-fat foods and, therefore, increase risk of heart disease, high cholesterol, liver and kidney damage, some cancers, and osteoporosis. How realistic is it never to have fruit or cereal for breakfast or a sandwich for lunch? The authors claim success through testimonial anecdotes and book sales. No scientifically validated studies suggest that this diet works.

• Eat Right 4 Your Type (Dr. Peter D'Adamo)

  Premise: The author, Dr. D'Adamo, claims that each blood type has its own unique antigen marker that reacts in negative ways with certain foods, and individuals have varying levels of stomach acidity and digestive enzymes that seem to correlate with blood type. This diet provides a detailed list of foods to eat or avoid, depending on your blood type.

  Facts: Although you may find it comforting to have a list of foods to eat or avoid, there's no scientific evidence that diets should be based on blood type.

• Suzanne Somers' Get Skinny on Fabulous Food (Suzanne Somers and associates)

  Premise: Suzanne Somers — actress turned health-products merchandiser, selling wares from skin care goods to pasta — says that when proteins and carbohydrates are eaten together their enzymes cancel each other out, creating a halt in the digestion process and causing weight gain.

  Facts: Reality check — many healthy, naturally occurring foods contain both carbohydrate and protein: nuts, milk, lentils, beans and whole-grain breads. This high-fat diet may put you at increased risk of coronary heart disease, high-cholesterol, liver and kidney damage, some cancers, and osteoporosis. There are no scientific studies to show that this diet works or is safe.

• New Diet Revolution (Robert C. Atkins, M.D.)

  Premise: The 1997 book, Dr. Atkins' NEW Diet Revolution, suggests drastically reducing the intake of dietary carbohydrates to force your body to burn your reserve of stored fat for energy. This results in losing pounds and inches while still eating protein and fat-laden foods. Meat, eggs, butter and most cheeses can be eaten without restriction on this diet.

  Facts: The effects of this high-protein diet actually may have you eating foods high in saturated fat, which may affect your blood cholesterol level and increase your risk of heart disease. There are no long-term studies to show that this diet works or is safe.

• Picture Perfect Weight Loss (Dr. Howard M. Shapiro)

  Premise: Dr. Shapiro's series of books feature photographs of food equations to help readers find low-calorie substitutes for the fattening foods that they crave. Pictures reveal that one candy bar contains the same amount of calories as 10 Popsicles. In addition to learning how one food's calorie content compares with another, readers are presented with correct serving sizes.
   

  Facts: Pictures don't necessarily translate into action. While not a complete solution, Shapiro's comparisons may be a starting point to help put the foods you eat into a useful, nutritional perspective.

• Protein Power Lifeplan (Michael R. Eades, M.D., and Mary Dan Eades, M.D.)

  Premise: Protein Power Lifeplan, published in 1997, and its proponents claim that the human body has no physical needs for carbohydrates and that they should be severely limited in order to trick your body into burning fat without making you feel hungry. Authors Drs. Michael and Mary Dan Eades make the case that you cut most carbohydrates out of your diet. A few menu choices include smoked salmon and cream cheese omelets, sauteed jumbo shrimp, and double-patty burgers.

  Facts: This high-protein diet may result in you eating high-fat foods and, therefore, increase your risk of heart disease, high-cholesterol, liver and kidney damage, some cancers, and osteoporosis. The authors claim success through testimonial anecdotes and book sales. No scientifically validated studies suggest that the Protein Power diet works.

• Revolutionary Weight Control Program (Bob Arnot, M.D.)

  Premise: In this diet, foods are considered drugs. Dr. Arnot, former chief medical editor for "NBC Nightly News," promotes a "feedforward" eating plan that teaches you in what order and at what times of day to eat foods to maximally control your weight, hunger and mood.

  Facts: Though foods containing soluble fiber are mentioned, other carbohydrate-containing foods are limited and along with them, their vitamins, minerals and phytochemicals. No scientifically validated studies have been conducted on Dr. Arnot's eating plan. Dr. Arnot's validation for his book comes from his friends and relatives.

• Sugar Busters! (H. Leighton Steward and associates)

  Premise: Sugar Busters! recommends cutting sugar in refined and processed forms from the diet. This includes: potatoes, white rice, corn, white bread beets, carrots and sugar honey, corn syrup and foods containing them. The authors claim that sugar is toxic to the body, causing the body to release insulin and store excess sugar as body fat.

  Facts: Long-term effects of high-protein, high-fat intake may include kidney and liver damage, heart disease and cancer. Sugar Busters! is supported by testimonials of the authors' believers and anecdotal claims. Its validity is based on opinions, not proven facts.

• Volumetrics (Barbara J. Rolls and associates)

  Premise: As the name implies, Volumetrics emphasizes eating high-volume, low-calorie foods and thereby getting full faster on fewer calories. High-volume foods take up more space, take a long time to eat and are often high in water content. You're still getting full, but on fewer calories, which adds up to weight loss.

  Facts: This program is based on research showing that eating high-volume, low-calorie foods can be an effective tool to decrease calorie intake, but the most effective weight-loss programs balance a healthy eating plan and exercise.

• The Zone diet (Barry Sears, Ph.D.)

  Premise: In his 1995 book, Enter the Zone, Sears writes that to enter "the zone" you need to eat the proper quantities of food, in the proper "macronutrient blocks" at prescribed times. Meals should contain carbohydrates, proteins and fats in the ratio of 40 percent, 30 percent, 30 percent, respectively. A sample meal may be 2 cups of pasta (carbohydrate), a 3-ounce piece of steak (protein), and a small handful of nuts or other fats to round out the meal.

  Facts: Although not as restricted as other high-protein, low-carbohydrate diets, the typical zone diet contains less than 1,000 calories, which may result in an inability to meet vitamin and mineral needs for most people. The Zone diet has not been validated scientifically. There's no scientific reason for eating set combinations of foods at set times.